1. Statement of the Technical Field
The inventive arrangements relate to methods and systems for adapting antennas for various operating conditions, and more particularly for adapting a whip type antenna to a dipole antenna having either a flat-top, inverted-L or inverted-V configuration.
2. Description of the Related Art
A whip antenna generally consists of a single driven linear element, which may be formed of a flexible rod member. The rod member is sometimes mounted above a ground plane for improved performance. A whip or monopole antenna has an omni-directional radiation pattern, meaning that the radiation gain is the same in all azimuth directions. The gain tends to diminish with increasing elevation angle, such that antenna gain is practically zero in a direction aligned with the axis of the antenna. While this arrangement works well for many applications, it is not well suited for Near Vertical Incidence Skywave or NVIS communications.
A portable vertical whip or monopole antenna is frequently used with various portable manpack transceivers. One such portable vertical whip antenna is an AT-271 antenna (also known as AS-271/PRC; National Stock Number NSN 5820-00-242-4967). Maximum range of ground-wave communications with a portable whip antenna such as the AT-271 is typically about 15 miles on the battlefield. However, modern battlefield doctrine also uses HF manpack transceivers for communications in the range of 25-200+ miles. Such distances require an antenna capable of NVIS (overhead pattern) performance.
For reasons explained above, vertical monopole antennas like the AT-271 are not generally suited for NVIS communications. Other antennas, such as the AS-2259 antenna system (also known as the AS-2259/GR; NSN 5980-00-106-6130) are well suited for NVIS; however, the AS-2259 is generally shunned due to its weight and bulk. Manpack HF transceivers are designed for users who operate in what the military refers to as “dismounted” configuration, i.e. a soldier with a radio on his back. Most HF dismount use has an element of covert or inserted operation. As such, these operations require small/light and quick to deploy antennas for which the AS-2259 is not well suited. Both the AT-271 and AS-2259 are produced many manufacturers but their design is dictated by military specifications.
A simple wire dipole type antenna can work well for NVIS communications. However, wire antennas of this kind have limited performance if they are too close to the ground. In many tactical environments, the absence of suitable support structures means that a wire dipole antenna will either be placed directly on or just a few inches above the ground. The result is relatively poor antenna performance. Wire antennas can be raised up above the ground if support structures are present. However, such support structures are often heavy and bulky, making them impractical to carry.
The RF-1942 (RF-1942-AT001) is a military HF vehicular antenna kit which can be configured in several different ways for different operational scenarios. The antenna includes a plurality of composite tubular sections that can be threaded together to form a whip antenna. The antenna kit also includes an inverted “V” component which is used to convert the whip antenna to an inverted “V” configuration. The inverted “V” component consists of a insulated winder structure onto which two wire antenna elements can be wound when stored. The winder structure is essentially a solid block of insulating material which is fixed to a female threaded element. The female threaded element can be screwed onto a male threaded element at the top end of the whip antenna.
One problem with the RF-1942 concerns deployment of the wire elements used to form an inverted “V” antenna. The wire elements which form the inverted “V” inevitably become twisted when unwrapped from the winder structure. The twisted wires are difficult to deploy and have a tendency to become tangled. This problem is compounded when the winder element is threaded onto the top end of the whip antenna. The problem is also compounded due to a downlead portion of one of the wire elements which extends adjacent to a length of the whip antenna to an antenna feed point. Once the winder is tightly threaded onto the top of the whip antenna, it is substantially fixed in position relative to the whip. In other words, the winder is not generally free to rotate around the whip. Consequently, when wire dipole antenna elements are deployed from the rigid and fixed structure of the winder, the wire elements forming the dipole antenna cannot be freely rotated around the axis of the whip antenna for purposes of facilitating deployment. This can be nuisance when trees or other obstacles interfere with deployment of the wire elements. Moreover, the down-lead element of the RF-1942 which extends along the length of the whip is formed as one continuous element with one of the dipole elements. This continuous element is threaded through the winder. Consequently, any rotation of the winder structure that does happen to occur will result in the down-lead component becoming wrapped or twisted around the whip antenna. As a practical matter, this arrangement tends to be inconvenient to deploy in the field.